Better Roads Staff
“It is important to first have an understanding of the shortcomings of both the conventional compaction equipment and QC practices currently being used in order to comprehend the role that IC can take in improving QC of HMA paving,” say Horan, Chang, Xu and Gallivan. “First, there are shortcomings in the conventional compaction process itself. Conventional compaction equipment does not allow for any, or very little, ‘on-the-fly’ feedback to project personnel.”
Typically, using a standard vibratory roller, a fixed number of passes are applied to the material being compacted. The problem is that critical factors can vary during construction, including support from underlying materials, lift thickness, materials type and asphalt mat temperature, the authors write.
“This software is a great first step in addressing one of the biggest barriers to IC implementation.”
The changes in these critical factors are invisible to the roller operator during conventional compaction operations.
The result is that either too little or too much compaction effort may be applied to the pavement material, says the report. IC provides a better method because constant information is continually reported to the roller operator related to pass count, the in-place pavement material density levels, or other density-related properties such as material stiffness.
“The second major shortcoming of conventional compaction equipment is that overcompaction can easily occur, and actually reduce the density that has already been obtained with previous passes,” the authors say. “Overcompaction occurs when pavement materials that are already adequately compacted have one or more additional passes of a vibratory roller. When this occurs, displacement of the material does not occur and the vibratory roller can enter into the undesirable ‘double jump’ mode where the roller is perceptively or imperceptibly bouncing on the pavement surface. This roller mode can be destructive to the pavement and actually cause a reduction in material density (and shear failure/dilation in soil materials).”
It’s also possible to undercompact pavements, they say. “This occurs when insufficient compactive effort is applied,” they write. “IC would provide a better method to help the roller operator avoid overcompaction (and undercompaction) by providing continual feedback that allows the operator to obtain the optimum number of roller passes. IC is able to address both shortcomings in current QC methods by providing the roller operator and QC personnel with access to unprecedented insight into the compaction process.”
The paper was based on the new Intelligent Compaction Pooled Fund (ICPF) project, No. 954, Accelerated Implementation of Intelligent Compaction Technology for Embankment Subgrade Soils, Aggregate Base, and Asphalt Pavement Materials, completed July 2011.
The immediate benefits include:
• real-time feedback to the roller operator,
• permanent records of compaction data,
• statistical and geospatial analysis of IC data, and
• mapping of underlying materials prior to paving/compaction.
New IC tools available to contractors and agencies include onboard, color-coded displays, capability to measure underlying material support prior to paving, and capability to collect data for statistical analysis of the effectiveness of compaction operations.
As part of the ICPF, a software program named Veda was developed that is designed to manage and evaluate IC data. “This software is a great first step in addressing one of the biggest barriers to IC implementation, which is a myriad of issues related to handling the massive amount of data produced during the compaction process,” the authors say. “The Veda software is available to the public.”
“The ecological benefits of pervious concrete can be taken a step further by incorporating recycled-concrete aggregate (RCA) into the mix design.”
A case study of the Wisconsin ICPF research was profiled to demonstrate how IC can improve QC of HMA paving. The project consisted of a two-lift HMA overlay on rubblized concrete pavements. Based on the ICPF findings, the authors concluded if IC had been used for the entire project, it could have:
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